Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Manichæan Controversy.: Chapter 22

Chapter 22.—The Form of the Region of Light the Worse of the Two.

Well, then, if this is so, the region of darkness is clearly touched on two sides by the region of light.  And if it is touched on two sides, it must touch on two.  So much for its being on one side, as we were told before.

24.  And what an unseemly appearance is this of the region of light!—like a cloven arch, with a black wedge inserted below, bounded only in the direction of the cleft, and having a void space interposed where the boundless emptiness stretches above the region of darkness.  Indeed, the form of the region of darkness is better than that of the region of light:  for the former cleaves, the latter is cloven; the former fills the gap which is made in the latter; the former has no void in it, while the latter is undefined in all directions, except that where it is filled up by the wedge of darkness.  In an ignorant and greedy notion of giving more honor to a number of pans than to a single one, so that the region of light should have six, three upwards and three downwards, they have made this region be split up, instead of sundering the other.  For, according to this figure, though there may be no commixture of darkness with light, there is certainly penetration.